1. Technical Field
This application relates to a device for the thermal deburring of workpieces.
2. Background Information
In thermal deburring plants, the workpieces to be deburred are accommodated in a combustion chamber. Once the combustion chamber is closed, a combustible gas mixture is introduced, for example an ignitable mixture of methane gas and oxygen. The mixing of the gas components usually takes place in a so-called mixing block, which is placed upstream of the combustion chamber. Serving for the introduction of the gas mixture is a gas supply duct, which opens directly into the combustion chamber in the usual manner. The gas mixture is ignited by a spark plug present in the mixing block. The flame front advances from the ignition point in the ignition channel of the mixing block via the gas supply duct into the combustion chamber and ignites the gas mixture present therein. The process is completed within just a few milliseconds. As a result of the heat given off, temperatures of up to 3,500° C. briefly occur in the combustion chamber. Following the ignition of the gas mixture, the pressure in the combustion chamber increases due to an isochoric reaction, which pressure increase is dependent on the charging pressure of the combustion chamber and the energy content of the gas mixture. Shortly after the ignition of the gas mixture in the combustion chamber, pressures in the order of magnitude of up to 1,000 bar can hereupon be generated due to the explosion. As a result of the resulting heat shock to which the workpieces are thereby exposed, the corners and edges thereof are eroded, since these points, with a large surface area and small volume, absorb a large amount of heat and are thus oxidized or burnt. In thermal deburring, the machining result to be obtained with respect to the workpiece is influenced by means of the quality (for example the mixing ratio) and the quantity (for example the charging pressure) of the gas mixture. A thorough and economical deburring of such workpieces is thereby possible without the need to use an expensive special tool or perform a tedious reworking by hand.
It is known that good and consistent results with respect to the deburring can only be realized if the correct composition of the combustible gas mixture with a predetermined charging pressure is present in the combustion chamber. This leads to sometimes considerable technical preparations having to be made to prepare the device for the thermal deburring for different workpieces.
In general, devices for treating a workpiece under a high pressure (of more than 200 bar, for example) normally have a machining chamber, which comprises a type of bell and a closing plate, which with a predefined closing pressure closes off an opening in the bell. The chamber is connected to a supply duct for supplying a fluid (liquid, gas, etc.) with a charging pressure and to the closing construction. During the machining, the closing plate is forced with a closing cylinder against the opening in the bell. The closing or clamping force is used to define the conditions in which the chamber, where necessary, is opened, for example when a destruction of the pressure vessel as a result of excessive charging pressures or the resulting explosion forces, and thus a threat to the environment, is to be feared. In many types of plant, this clamping force is kept constant. The counterforce resulting from the machining of the workpiece is dependent on the cross section of the chamber or bell, so that, specifically in the case of round chamber shapes or round openings which are closed with the closing plate, it is made easier to gear to the diameter thereof. This counterforce is quadratically dependent on the chamber diameter, so that, as the chamber diameter becomes larger, the maximally permitted charging pressure falls. This means with regard to the thermal deburring, for example, that combustion chambers having a large combustion chamber diameter are normally unsuitable for deburring small bores on workpieces, since the high energy per unit cross-sectional area of the combustion chamber which is necessary for this purpose can no longer be achieved. For such treatments of a workpiece under high pressure, respectively separate devices, each having a different chamber diameter and/or a different closing constructions, have hitherto been used.
For the thermal deburring of workpieces, safety devices, such as hydraulic pressure relief valves, may be installed to prevent the deburring chamber from exposure to pressures greater than its design limits. In the case of the present application, the setting of these safety devices is substantially dependent on the size of the deburring chamber, where size refers to the diameter of the deburring chamber. In other existing means of deburring workpieces, to change the size of chamber in use requires re-adjustment of the safety devices. However, the user of the machine may not be permitted to carry out this adjustment due to some type of restrictions, such as in Europe, for example, where the setting of the safety devices must be certified by an independent Notified Body. At least one possible embodiment of the present application may allow the user of the TEM machine to change the size of the deburring chamber without the assistance of the manufacturer and without the need for certification from a Notified Body. This may be achieved, in at least one possible embodiment of the present application, by having multiple safety devices on the device for thermal deburring of workpieces—one for each deburring chamber size that the customer wishes to use. In order to maintain the required level of safety, it must be ensured that the correct safety device is applied for each deburring chamber when installed in the machine. Therefore, a secure means of detecting the deburring chamber size installed and a secure means of selecting the compatible safety device are essential.